The users of key telephone systems and private branch exchanges find the station message detail recording (SMDR) feature a desired capability to monitor, control and plan the telecommunication budget. In the SMDR units of large PBXs, direct distance dial (DDD) calls are priced using the standard FCC tariff No. 263 which considers various call parameters such as distance, time of day and length of the call. While the time of day and length of the call can be readily determined, the calculation of calling distance requires the system to store vast quantities of data. This data base includes data on the approximately 10,000 central offices and their V and H geographic coordinates along with the pricing schemes for the various interstate and intrastate carriers.
Small key telephone systems, however, do not have a sufficiently large memory to store the vast amount of V and H coordinate data required to establish the price of telephone calls using the conventional method. Prior art SMDR systems attempt to compress the V and H data required for determining calling distances.
In one type of SMDR system the calling distance between a customer's communication system and each central office (NNX) in a number plan area (NPA), i.e., area code, is determined and each NNX is assigned to one of the standard fixed calling rate bands. When all of the NNXs in a NPA can be assigned to the same rate band, the NPA can be "compressed" into one pair of V and H coordinates which can be used for all calls to that area code. However, if some NNXs of the NPA fall into different rate bands the data cannot be compressed and each NNX and its V and H coordinates within the NPA must be stored as a comprehensive list. Disadvantageously, this type of SMDR system requires that the compressed data base be individually determined and entered into memory for each communication system. Moreover, this compressed data base must be updated when new NNXs are added by the local telephone companies.
What is desired is a method and apparatus for establishing the price of telephone calls which reduces the size of the data base required and which minimizes the amount of customer programming and data base maintenance.